Wireless CCTV

Monitoring lightning protection

2016/03/04

I. Overview

       We know that whether it is the variable magnetic field generated by lightning in the pilot channel or the return channel of the space, or the variable magnetic field generated by lightning after entering the lightning rod system of the ground building, it will produce electromagnetic effects in a certain space. It can be the electromagnetic induction effect determined by Faraday's law of electromagnetic induction, or it can be pulse (commonly used by LEMP) to affect all electronic devices in the three-dimensional space, generate induced current in a closed metal loop, or not close. In the conductor loop, a high induced voltage is generated. According to the CCIT test, the induced current on the general power line is about 3000 amps, no more than 10 kA, and the induced voltage does not exceed 6 kV. On the data signal line and the telephone line, the induced voltage is generally around 5 kV. The induced current is about several hundred amperes. This makes it easy to discharge sparks at the gap, causing a fire. When lightning passes through the lightning rod to lead the line, a strong variable pulse electromagnetic field will be generated in the space nearby. When the magnetic pulse exceeds 0.07 gauss, the computer will fail. When it exceeds 2.4 gauss, the induced integrated circuit will be permanently damaged, especially for VLSI. With the development of science and economy, the application of computers in various industries has become very common. Many daily affairs depend to a large extent on computer systems. A little carelessness, lightning disasters will lead to paralysis of the entire system.

Second, the main basis

1 National Standard of the People's Republic of China GB50074-94 "Code for lightning protection design of buildings"

2 International Electrotechnical Commission IEC1312-1~3 "Protection of Lightning Electromagnetic Pulses"

3 National Standard of the People's Republic of China GB50174-93 "Design Specification for Electronic Computer Room"

Third, technical measures

In accordance with the principle of overall lightning protection. In combination with modern lightning protection technology, according to the principle of lightning electromagnetic pulse (LEMP) protection, we consider from the three main interference sources of operating voltage (SEMP) and electrostatic discharge (ESD) in LEMP and power network. Take measures in terms of power supply and signal:

  1. Power lightning protection

(1) Install a three-phase power supply lightning protection box in front of the power distribution cabinet to attenuate the strong lightning current and high voltage introduced by the power line.

(2) In the monitoring system room power supply line distribution box air switch end, and connected to the three-phase power supply lightning protection device, with light alarm and lightning strike counting function, further attenuating the strong lightning current and high voltage introduced from the power line, protection Power supply safety for the entire equipment room system.

(3) Connect the power supply lightning protection socket in front of the machine room to ensure the safety of the host.

(4) Connect the power supply lightning protection sockets in front of the display to ensure the safety of each display and each electrical equipment.

(5) Adding a power supply lightning arrester at each power supply line of the ball type camera to effectively attenuate the lightning current and lightning voltage introduced from the power line to protect the safety of the camera gun.

(6) Install a DC 12V power supply arrester before each power supply of the 12V power camera gun, effectively attenuating the lightning current and lightning voltage introduced from the power line to protect the security of the camera gun.

  2. Signal lightning protection

One-to-one video transmission between the peripheral monitoring and monitoring center. In order to better play the overall lightning protection effect, the camera gun and the monitoring center are in a one-to-one correspondence relationship. Signal arresters are installed on both ends of the host and the camera gun to protect the safety of the monitoring center and the camera gun.

(1) Install an information line protector on both ends of the video line of the camera gun to attenuate the lightning voltage and lightning current induced on the video line.

(2) Install a control signal protector on both ends of the camera gun pan/tilt control line to attenuate the lightning voltage and lightning current induced on the control signal line.

3. The monitoring center room is an independent grounding body.

In the construction of the computer room, there must be a good computer room independent system. Do a good job in the construction of the grounding system of the equipment room to ensure the safety of equipment and personnel, and to make the equipment of the equipment room work stably and reliably. If the grounding system of the equipment room is not well done, it will not only cause equipment failure, but also burn out the components, which will seriously endanger the safety of the workers.

(1) Grounding body selection

According to different geographical environments, the grounding body can be selected in various shapes. According to actual experience, the grounding module should be used.

(2) Grounding body requirements

Grounding resistance requirements:

Ra≤1Ω

(3) Technical measures

Using the Tiandun grounding module to reduce the grounding resistance is a common scientific method used in grounding engineering. According to the soil condition, an appropriate amount of grounding module can be installed to achieve the grounding resistance R≤1Ω. The use of a grounding module to reduce the resistance not only minimizes the grounding resistance, but also ensures that the grounding body remains stable for a long period of time. Its useful life is greater than 30 years. It has moisture absorption and moisturizing properties, low grounding resistance and long-term stability. After repeated high-current impact, the resistance does not increase, and there is no hardening, brittleness or fracture. Compared with the resistance-reducing agent, it has obvious Superiority; can withstand low temperatures of -40 ° C, the same applies to the northern cold regions.

(4) Description

It consists of non-metallic minerals and electrolytic materials with good conductivity and stability. Its birth has created a new era of grounding materials and grounding technology.

The common grounding body is mostly a metal conductor, and the most common ones are angle steel, round steel, steel pipe, copper rod, copper mesh, and the like. It is characterized by more materials, high cost, short life, poor stability, and is not suitable for use in areas with high soil resistivity. The grounding module is less suitable for use in high resistivity soil areas due to less material consumption, low cost, long life (up to 30 years) and good stability. If the grounding point is surrounded by sandstone or rock formation, it can be used to form a special "artificial ground" to solve some difficult problems in grounding work, and this product is non-polluting, non-toxic, anti-corrosive and easy to use.

The basic reason why the grounding module can obtain low grounding resistance is that in the same external dimensions, the metal material is doubled to increase the contact area between the grounding body and the soil layer, thereby increasing the scattered area of the grounding body itself; It reduces the contact resistance between the grounding body and the soil; it has strong hygroscopicity and moisture retention, and fully exerts the conductive effect of the electrolytic substance in the grounding body.


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